Normal state spectral lineshapes of nodal quasiparticles in single layer Bi2201 superconductor

Abstract

A detailed study of the normal state photoemission lineshapes and quasiparticle dispersion for the single layer Bi2Sr2−xLaxCuO 6+δ (Bi2201) superconductor is presented. We report the first experimental evidence of a double peak structure and a dip of spectral intensity in the energy distribution curves (EDCs) along the nodal direction. The double peak structure is well identified in the normal state, up to ten times the critical temperature. As a result of the same self-energy effect, a strong mass renormalization of the quasiparticle dispersion, i.e. kink, and an increase of the quasiparticle lifetime in the normal state are also observed. Our results provide unambiguous evidence on the existence of bosonic excitation in the normal state, and support a picture where nodal quasiparticles are strongly coupled to the lattice. PACS numbers: 74.25.Jb, As a measure of the imaginary part of the single particle Green's function, photoelectron spectroscopy provides insights on the scattering processes that play a key role for the physical properties of a material. In a metallic system for example, the coupling of quasiparticles to phonons causes the photoemission line shape to evolve from a single Lorentzian-like peak, as for a Fermi liquid picture, to double or multiple peak structures [2] with a dip of spectral intensity, which correspond to the phonons energy. The coupling to phonon, or more in general to any bosonic excitation, is also reflected in a renormalization of the quasiparticle dispersion, and in an increase of the quasiparticle lifetime below the phonon energy [3]. In the framework of quasiparticles coupled to a bosonic excitation these behaviors are the result of the same selfenergy effect, Σ(k, ω), and occur at a similar energy scale [4].This textbook behavior has been recently measured by angle resolved photoemission spectroscopy (ARPES) in several systems characterized by a strong electronphonon interaction, such as Be [5], Mo [6], W [7] and C 60 [8]. Similar behavior has also been observed in several families of p-type cuprates along the nodal direction, (0, 0) to (π, π) [9,10,11,12,13,14,15,16]. While in the case of simple metals the interpretation is straightforward and phonons are easily identified as the relevant energy scale, the interpretation is far more complex in the case of strongly correlated systems as cuprates superconductors. Although the experimental data between different groups are in agreement, and are in favor of a scenario of quasiparticles coupled to bosonic modes, the nature of such excitations is still highly controversial and has been matter of intense study over the last few years.The two proposed scenarios see quasiparticles coupled to phonons [10,11] vs quasiparticles coupled to an electronic mode [12,13,14,15,16]. On the basis of energy scale it has been argued that, the highest energy phonon coupled to quasiparticle is the in plane half-breathing oxygen phonons [17,18], while the relevant electronic mode is the (π, π) resonance mode, observed by neutron scattering [19,20]....

Through a Lattice Darkly: Shedding Light on Electron–Phonon Coupling in the High-Tc Cuprates

“…In favor of the electron-phonon coupled system is the drop of the quasi-particle width ( Fig. 3) below the kink energy and the existence of a well-defined peak-dip-hump in the EDCs, a signature of an energy scale within the problem, persisting up to temperatures much higher than the superconducting critical temperature [15].…”

Through a Lattice Darkly: Shedding Light on Electron-Phonon Coupling in the HighTcCuprates

“…In favor of the electron-phonon coupled system is the drop of the quasi-particle width (Figure 3) below the kink energy and the existence of a well-defined peak-dip-hump in the EDCs, a signature of an energy scale within the problem, persisting up to temperatures much higher than the superconducting critical temperature [15].…”

Analysis of the spectral function ofNd1.85Ce0.15CuO4obtained by angle-resolved photoemission spectroscopy

“…10 Sudden changes in the slope in the band dispersion observed via ARPES allow one to infer the underlying physics causing these renormalizations. 10 Low-energy renormalizations have been prevalently found in the nodal region of p-doped cuprates via ARPES, 10,11 but not in the nodal region of n-doped cuprates, 5 casting doubt on the universality of the renormalization effect in the cuprates for the whole phase diagram.…”

“…1͑b͒ and 1͑d͔͒. 11 Within the context of electron-phonon interaction, a renormalization at around 70 meV is seen in the nodal region of p-doped HTSCs in ARPES and has been attributed to electron-phonon interactions. 10,26 A softening of an oxygen mode was seen as well for the n-doped compound NCCO via inelastic neutron and x-ray scattering ͑55 meV͒, 23,27 and now also in the nodal region via ARPES as observed by us in the same relevant energy region.…”